1. Field of the Invention
The present invention relates to an exposure method which is particularly useful in the manufacture of devices that are relatively large in area, e.g., liquid crystal devices by lithographic techniques and more particularly to an exposure method for exposing a plurality of abutting subdivision patterns so as to effect the exposure of a large-area pattern made by composing (stitching) images and apparatus therefor.
2. Description of the Prior Art
In the past, in the manufacuture for example of liquid crystal panel devices or the like for display units, there has been used a method in which while changing a plurality of original image reticles, the original image patterns of the respective reticles are stitched together by image composition and the resulting large-area composite image pattern is exposed onto a substrate. In this case, under the ideal alignment conditions a single composite image is composed of the subdivision areas or the effective exposure zones of the respective original images which have been accurately abutted and composed or stitched together without any gaps or overlaps.
In other words, at least one alignment mark is formed at the same design position on each of the individual reticles and an alignment is effeced by the reticle alignment systems in such a manner that the alignment mark of a reticle carried on the reticle holder of an exposure apparatus comes into registration with the alignment reference mark of the apparatus on the reticle holder.
A substrate subject to the exposure is held on a movable stage and the movement of the stage is subjected to position control by laser interferometers. After the exposure of one reticle has been effected, the exposure to the abutting area is effected according to the next reticle. In this case, the movement of the stage is of course controlled to the distance corresponding to the size of the subdivision area exposed previously.
With the conventional techniques, it has been usual so that where the alignment marks of the individual reticles involve positional faults due to errors caused during the manufacture, etc., (including any positional fault within the reticle plane and any positional fault in the thickness direction due to variations in the reticle thickness), there are mark detection errors, etc., due to the reticle alignment systems, or there are any distortion of the projected image due to the remaining imaging characteristic error components (e.g., projection magnification errors, distortions, etc.,), the subdivision areas are caused to shift in position in the x or y direction relative to each other, or rotational errors are caused relative to each other or they are distorted, thus failing to attain an accurate abutting composition. Thus, there is the disadvantage of deteriorating the quality of the whole area of the resulting device such as a liquid crystal panel.